JPH04363251A - Ink jet recording method - Google Patents

Abstract

PURPOSE:To obtain a stable image without causing the consumption of electricity to increase and without being affected by exterior environment by applying to a heater a pulse smaller in energy than a printing pulse before applying the printing pulse. CONSTITUTION:An ink jet recording is effected by applying a printing pulse to a heater provided on a base plate and flying ink drops onto a recording medium by the pressure of the vapor bubbles formed under heat produced by the heater. Before applying the printing pulse, a pulse 21 smaller in energy than the printing pulse 20 is applied to the heater. The temp. of ink near the heater is raised by the heater energized by the pulse 20 to permit the volume of the bubbles being formed to increase. In this way the volume of the ink drops to be injected can be increased. The pulse 21 to be applied before the printing pulse may be applied only when ambient temp. is low.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an inkjet recording method in which recording is performed by jetting ink drops using the pressure of vapor bubbles generated by heat generated by a heater.

(Prior Art) In the inkjet recording method, the thermal intanite recording method, in which ink drops are ejected by the pressure of vapor bubbles generated by heat generated by a heater, is capable of high-density and high-speed recording due to its structural characteristics. , it is extremely easy to realize a multi-nozzle head.
It has been attracting attention in recent years.

In such a thermal inkjet recording method, the physical properties of the ink and the state of bubble generation change depending on the operating environment temperature, particularly the temperature of the ink in the head, and as a result, the amount of ejected drops changes. therefore,
There are problems in that the image density changes depending on the environmental temperature, and in the worst case, gaps occur between dots during solid printing, resulting in significant deterioration of image quality.

As a method to solve this problem,
Publication No. 252 describes a method in which a temperature sensor and a heat generating means are installed in the head section, and the temperature of the entire head is raised to a constant temperature when the temperature is low.

However, this method heats the entire head,
There are problems in that the size of the added heater increases, the overall size of the head increases, and power consumption increases because ink inside the head is heated from outside the head.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned problems.
It is an object of the present invention to provide an inkjet recording method that can obtain stable image quality without significantly increasing power consumption and without being affected by external environmental temperature.

(Means for Solving the Problems) The present invention applies a printing pulse to a heater provided on a substrate, and uses the pressure of vapor bubbles generated by the heat generation to cause ink drops to fly onto a recording medium to perform recording. The inkjet recording method is characterized in that, before applying a printing pulse, a pulse (preceding pulse) having smaller energy than the printing pulse is applied to the heater.

As the preceding pulse, a pulse having a lower voltage than the printing pulse can be applied.

As the preceding pulse, a pulse having a smaller pulse width and voltage than the printing pulse can be applied.

When a preceding pulse is applied prior to a print pulse based on the image signal, one or both of the width and voltage of the print pulse can be changed.

The preceding pulse may be applied when the carriage temporarily returns to its home position or when the direction of travel of the carriage is reversed.

(Function) FIG. 3 is a sectional view showing a schematic configuration of a head section of a thermal inkjet printer used in an embodiment of the present invention. In the figure, 1 is a channel substrate, 2 is a heater substrate, 3 is a heat storage layer, 4 is an ink flow path, 5 is an ink supply port, 6 is a nozzle, 7 is a thick film insulation layer, 8 is a protective layer, and 9 is an insulation layer (protective layer), 10 is a heater layer, 11 is an electrode layer, 12 is an insulating layer,
13 is a pit. The dimensions of this thermal inkjet head are 110 μm from the heater to the nozzle;
The distance from the heater to the ink supply port is 130 μm, the heater size is 45 μm×110 μm, and its resistance value is 130 Ω at room temperature.

When a pulse with a pulse width of 3 μsec and a voltage of 32 V was applied to this heater section at a repetition frequency of 3 kHz,
At an ambient temperature of 30° C., a drop with a volume of 80 pl was obtained. However, at an environmental temperature of 15° C., when a pulse under the same conditions was applied, a drop with a volume of only 56 pl was obtained, and the dot density on the paper decreased.

FIG. 2 shows the time course of the applied voltage, the temperature at the interface between the heater and the ink, and the bubble volume, where a is the applied voltage and 20 is the printing pulse. b is the temperature at the interface between the heater and ink, c
indicates the bubble volume.

In addition, when the environmental temperature is 30°C, the figure (A) is
B) is a graph when the environmental temperature is 15°C.

Based on this result, considering the reason why the volume of ink drop decreases due to a decrease in environmental temperature, it is possible that a decrease in ink temperature increases ink viscosity, which causes an increase in flow path resistance. In such a transient flow phenomenon, the effect of an increase in flow path resistance is small, and the effect is rather large because the bubble volume decreases due to a decrease in temperature and the bubble disappears earlier.

For this reason, in order to increase the drop volume, the influence of flow path resistance is small, so it is not necessary to heat the entire ink inside the head, but only the ink near the heater needs to be heated.

Therefore, as shown in FIG. 2(C), prior to the printing pulse 20, a pulse 21 is applied to such an extent that no bubbles are generated. The heat generated by the heater due to the pulse 20 can raise the ink temperature near the heater, increase the volume of generated bubbles, and delay the time at which the bubbles disappear. This makes it possible to increase the volume of the drop to be ejected.

Prior to the printing pulse, the pulse may be applied only when the environmental temperature is low. or,
The energy of the previously applied pulse may be automatically changed depending on the environmental temperature.

(Example) FIG. 1 is an explanatory diagram of an example of the inkjet recording method of the present invention. The printing pulse 20 is given at a driving frequency f, and a preceding pulse 21 is applied prior to the printing pulse to an extent that no bubbles are generated.

When using the same head as described in FIG. 3, an example of the preceding pulse was a pulse with a pulse width of 15 μsec and a voltage of 10 V. When this pulse was applied to the heater, the printing pulse produced 78 pl even at an environmental temperature of 15°C.
drop and the same image quality as at 30°C. This is because, as explained in FIG. 2, the ink temperature near the heater rose compared to when no preceding pulse was applied, and the bubble volume increased.

FIG. 4 shows a method in which the presence or absence of a preceding pulse is used to give a larger width to the drop volume to express gradation.

Using the same head as explained in Figure 3, the ambient temperature was 25℃.
Printed under certain conditions.

When a printing pulse 20a with a width of 3 μsec and a voltage of 30 V was applied when there was no preceding pulse, a drop of 59 pl was obtained. Next, before the printing pulse, a pulse width of 20μse is applied.
c, a preceding pulse 21 with a voltage of 12 V was applied, and then a pulse 20b with a voltage of 28 V for 4.5 μsec was applied as a printing pulse, and a drop of 105 pl was obtained.

By using these two types of drops together with a 2×2 matrix dither method on paper, 16 gradations (3L method) could be obtained. According to this method, the resolution can be doubled compared to the conventional gradation expression method using a 4×4 matrix.

The composition of the ink used in these examples was 60% water
% by weight, diethylene glycol 38% by weight, and dye 2% by weight.

In the embodiment explained in FIG. 1, the preceding pulse for temperature increase was applied at low temperature, but it may be applied all the time.
Alternatively, the energy of the preceding pulse may be changed depending on the temperature.

In addition, although the preceding pulse was applied immediately before the printing pulse, when waiting for image data, when performing maintenance operations, or when the running direction of the carriage is reversed, printing may occur as shown in Fig. 5. For pulse 20,
A plurality of preceding pulses 21 may be applied in succession to raise the temperature of the ink near the heater.

(Effects of the Invention) As is clear from the above description, according to the present invention, it is possible to prevent changes in image quality due to environmental temperature changes with a conventional head configuration without adding a special temperature control device. effective.

Furthermore, by combining the preceding pulse with the recording pulse according to the image signal, it is possible to express a wide range of gradations without lowering the resolution compared to conventional gradation expression methods.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the inkjet recording method of the invention, FIG. 2 is an explanatory diagram of the operation of the invention, and FIG. 3 is a head of a thermal inkjet printer used in the embodiment of the invention. FIG. 4 is an explanatory diagram of an embodiment of the inkjet recording method of the present invention;
FIG. 5 is an explanatory diagram of another embodiment of the inkjet recording method of the present invention. 20, 20a, 20b...Print pulse 21...Prior pulse Patent applicant Fuji Xerox Co., Ltd. Agent Yasuo Ishii

Claims (1)

[Claims] In an inkjet recording method in which a printing pulse is applied to a heater provided on a substrate, and the pressure of a vapor bubble generated by the heat generation causes ink drops to fly onto a recording medium and perform recording, before applying a printing pulse, An inkjet recording method characterized in that a pulse of energy smaller than the printing pulse is applied to a heater.